Monitoring and analyzing nonlinear dynamics in atomic force microscopy

The nonlinear dynamics that have been predicted for intermittent contact mode Atomic Force Microscopy (AFM) in the strongly repulsive tip-sample interaction regime is analyzed and monitored. The experimental apparatus detects the raw cantilever response at all frequencies with an analog-to-digital converter. In the initial attractive regime of the tip-sample interaction, the cantilever oscillation amplitude decreases in a linear fashion. As the tip-sample interaction transitions to the repulsive regime, the raw cantilever oscillation data undergoes an abrupt change that includes more complicated substructure and nonlinear features. In this repulsive tip-sample interaction regime, many of the higher harmonics and subharmonics are greater than 10% of the amplitude at the driving frequency. The nonlinearities in other frequency-dependent AFM technique can similarly be characterized by monitoring and analyzing the entire frequency response, as opposed to only locking in to the driving frequency.